SLA downtime for child services is not calculated correctly

[MasterOfChilli]

Hello,

we are using the Zabbix Version 6.0.9.
Currently, we are monitoring our Citrix farm with this version.

I created a parent service (Citrix Worker SLA Monitoring) which contains all our citrix server as child services (Ping as problem tag).
The SLI and downtime (a few minutes per day cause our citrix servers get booted in the night) is correcty calculated for the Child Services.

However, the downtime for the parent service (Citrix Worker SLA Monitoring) is allways 0 and the SLI is 100%.
Why is the downtime allways 0 and not calculated from the child services?

My expectation would be that the parent service contails the summed up downtime from all child services or something like that.

Thanks in advance for any advices.

[MasterOfChilli]

Addendum: I changed the status calculation rule of my parent service to "Set status to ok" and under additional rules "If at least 1 child services have
average status or above set status to average ". I then shut down 2 of our
Citrix servers. Downtime is now added to my parent service. So far so good.

My question is now: If 2 or more servers are down at the
same time, only the downtime of one server is counted towards the parent service correct?

Is it possible that the downtime of multiple servers is counted together to my parent service if they are down at the same time?